Since microfabrication technology, material technology, and mounting technology have made progress in recent years, a liquid crystal display device characterized by light weight, thinness and small power consumption has been widely used as an image display device which replaces a Braun tube, in a variety of devices such as an audio-visual device, an office automation device, an in-vehicle device, an information-communication device and the like. A liquid crystal display module is mounted in these liquid crystal display devices for processing a driving signal to display an image.
In general, the liquid crystal display module comprises a liquid crystal display panel, a printed circuit board, and a flexible printed circuit board, and typically has a structure in which the liquid crystal display panel and the printed circuit board are electrically connected to each other by means of the flexible printed circuit board.
FIG. 12 is a view schematically showing a general structure of a liquid crystal display module L.
The liquid crystal display module L illustrated in FIG. 12 comprises a liquid crystal display panel 1 for displaying an image according to an applied driving signal, flexible printed circuit boards FPC1 to FPC4 for transmitting the driving signal to the liquid crystal display panel 1, and a printed circuit board PCB1 for processing the driving signal of the liquid crystal display panel L. The liquid crystal display panel 1 is provided with a display region 2 for displaying an image, and a non-display region 3 around the display region 2. And, driving semiconductor devices IC1 to IC5 are mounted at predetermined positions of the non-display region 3 for directly driving the liquid crystal display panel 1. Also, driving semiconductor devices IC6 to IC9 are mounted at predetermined positions of the printed circuit board PCB1 for processing the driving signal for driving the liquid crystal display panel 1. And, the liquid crystal display panel 1 and the printed circuit board PCB1 are integrated with each other by electrically connecting electrode terminals (not shown) formed on each of them by means of the flexible printed circuit boards FPC1 to FPC4. Herein, electrical connections between the liquid crystal display panel 1 and the flexible printed circuit boards FPC1 to FPC4 and between the flexible printed circuit boards FPC1 to FPC4 and the printed circuit board PCB1 are performed by electrically connecting electrode terminals to one another by means of an anisotropic conductive adhesive or the like. First, the flexible printed circuit boards FPC1 to FPC4 are bonded to the liquid crystal display panel 1, and then the flexible printed circuit boards FPC1 to FPC4 are bonded to the printed circuit board PCB1. A COG (Chip On Glass) mounting process in which the driving semiconductor devices IC1 to IC5 are directly mounted on the electrode terminals provided on a surface of the liquid crystal display panel 1 is commonly used as a process for mounting the driving semiconductor devices IC1 to IC5 on the surface of the liquid crystal display panel 1. As an alternative process for mounting the driving semiconductor devices IC1 to IC5, there is a TCP (Tape Carrier Package) mounting process in which a film board obtained by mounting the driving semiconductor devices IC1 to IC5 on a surface of a tape-shaped film wiring board provided with a predetermined wiring pattern is mounted on the surface of the liquid crystal display panel 1, a COF (Chip On Flexible) mounting process, a COP (Chip On Plastic) mounting process and the like, in which a flexible board obtained by mounting the driving semiconductor devices IC1 to IC5 on the flexible printed circuit board made of plastic is mounted on the surface of the liquid crystal display panel 1, for example. However, since the driving signal of the liquid crystal display panel increases as definition of a liquid crystal display device becomes higher, the COG mounting process is commonly used for reducing the electrode terminals formed on the liquid crystal display panel 1.
FIGS. 13(a) and 13(b) are enlarged schematic views showing the flexible printed circuit board FPC1 and the vicinity thereof of the liquid crystal display module L illustrated in FIG. 12, in which FIG. 13(a) is a plan view and FIG. 13(b) is a cross-sectional view taken along line A-A′ in FIG. 13(a). And, FIGS. 14(a) and 14(b) are views illustrated in association with the schematic views shown in FIGS. 13(a) and 13(b), schematically showing a condition before the liquid crystal display panel 1 and the printed circuit board PCB1 are integrated with each other by means of the flexible printed circuit board FPC1, in which FIG. 14(a) is a plan view and FIG. 14(b) is a cross-sectional view taken along line A-A′ in FIG. 14(a).
Hereinafter, the electrical connection between the liquid crystal display panel 1 and the printed circuit board PCB1 by means of the flexible printed circuit board FPC1 will be described with reference to FIGS. 13(a), 13(b) and FIGS. 14(a), 14(b). The flexible printed circuit board FPC1 in FIGS. 13(a), 13(b) and FIGS. 14(a), 14(b) is perspectively shown. X-axis, Y-axis, and Z-axis directions (Z-axis direction is a direction perpendicular to a drawing surface) in FIGS. 13(a), 13(b) and FIGS. 14(a), 14(b) are defined as shown in the drawings. As a matter of convenience, hereinbelow, it is assumed that a longitudinal direction and a lateral direction of the display region 2 of the liquid crystal display panel 1 conform to X-axis direction and Y-axis direction, respectively, in this embodiment.
As shown in FIGS. 13(a), 13(b) and FIGS. 14(a), 14(b), herein, the flexible printed circuit board FPC1 is rectangular and has a three-layer structure in which wiring patterns P1 to Pn obtained by forming copper foil in a predetermined shape by etching or the like, a cover film 5, and a base film 6 each of which is made of semi-transparent insulative resin such as polyimide are laminated. The wiring patterns P1 to Pn are formed to extend from one side of the flexible printed circuit board FPC1, which is parallel to X-axis direction, to the other side thereof to have substantially constant pattern widths and pattern spacings. And, rectangular conductive patterns P1a and Pna extend in opposite directions from side portions of the wiring patterns P1 and Pn on the liquid crystal display panel 1 side to be each spaced a predetermined distance apart from an end of the flexible printed circuit board FPC1. Furthermore, predetermined circular alignment markers N2 are formed on the conductive patterns P1a and Pna. And, as shown in FIG. 14(b), in the flexible printed circuit board FPC1, the base film 6 is rectangular shaped to have sides substantially parallel to two sides of the flexible printed circuit board FPC1 which are parallel to X-axis direction, with a predetermined distance therefrom. Thereby, end portions of the wiring patterns P1 to Pn are exposed so as to be electrically connected to external electrode terminals.
As shown in FIGS. 13(a) and 13(b), one end portion of the flexible printed circuit board FPC1 provided with the alignment markers N2 is bonded to a predetermined position of the liquid crystal display panel 1 by means of an anisotropic conductive adhesive 4A, after predetermined alignment with the liquid crystal display panel 1 to be described below is performed. As shown in FIG. 14(a), rectangular electrode terminals R1 to Rn for applying the driving signal to the liquid crystal display panel 1 are formed on a surface of the non-display region 3 of the liquid crystal display panel 1, which is covered with the anisotropic conductive adhesive 4A, at positions corresponding to the wiring patterns P1 to Pn of the flexible printed circuit board FPC1, so as to be substantially parallel to each other. Therefore, one end portions of the wiring patterns P1 to Pn provided on the flexible printed circuit board FPC1 are electrically connected to the corresponding electrode terminals R1 to Rn of the liquid crystal display panel 1. And, as shown in FIGS. 13(a) and 13(b), the other end portion of the flexible printed circuit board FPC1 is bonded to a predetermined position of the printed circuit board PCB1 by means of an anisotropic conductive adhesive 4B without special alignment with the printed circuit board PCB1, after the liquid crystal display panel 1 and the printed circuit board PCB1 are disposed so as to be in a predetermined positional relationship. As shown in FIG. 14(a), rectangular electrode terminals T1 to Tn for outputting the driving signal to the flexible printed circuit board FPC1 are formed on a surface of the printed circuit board PCB1, which is covered with the anisotropic conductive adhesive 4B, at positions corresponding to the wiring patterns P1 to Pn of the flexible printed circuit board FPC1, so as to be substantially parallel to each other. Therefore, the other end portions of the wiring patterns P1 to Pn provided on the flexible printed circuit board FPC1 are electrically connected to the corresponding electrode terminals T1 to Tn of the printed circuit board PCB1.
Hereinafter, an alignment process performed when the flexible printed circuit boards FPC1 to FPC4 are bonded to the liquid crystal display panel 1 will be described.
As shown in FIG. 14(a), two predetermined circular reference markers N1 are formed on the liquid crystal display panel 1, with a predetermined distance from a side of the liquid crystal display panel 1 which is near these markers N1. And, two predetermined circular alignment markers N2 are formed on the flexible printed circuit board FPC1 at positions corresponding to the reference markers N1 provided on the liquid crystal display panel 1. And, the alignment of the flexible printed circuit board FPC1 with the liquid crystal display panel 1 is performed manually or by an automatic alignment device or the like such that the centers of the alignment markers N2 and those of the reference markers N1 preferably conform to each other as shown in FIG. 13(a), or the reference markers N1 are located at least inward relative to the alignment markers N2. A diameter of the alignment markers N2 is preferably substantially equal to that of the reference markers N1 so as to prevent misalignment of the flexible printed circuit board FPC1 with the liquid crystal display panel 1 occurring when the flexible printed circuit board FPC1 is bonded to the liquid crystal display panel 1. However, in that case, recognition of relative positions of the alignment markers N2 with respect to the reference markers N1 becomes difficult, and consequently, it becomes difficult to efficiently perform the alignment between the liquid crystal display panel 1 and the flexible printed circuit FPC1. Accordingly, actually, as shown in FIGS. 13(a), 13(b) and FIGS. 14(a), 14(b), the diameter of the alignment markers N2 is made slightly larger than that of the reference markers N1 within a range in which the liquid crystal display panel 1 and the printed circuit board PCB1 are properly electrically connected to each other even when the bonding position of the flexible printed circuit board FPC1 is out of alignment in the above-described alignment process.
In the above-structured liquid crystal display module L, the driving signal processed at the driving semiconductor devices IC6 to IC9 is guided to the electrode terminals T1 to Tn formed on the printed circuit board PCB1, furthermore, guided through the flexible printed circuit boards FPC1 to FPC4 to reach the electrode terminals R1 to Rn of the liquid crystal display panel 1, and is inputted to the driving semiconductor devices IC1 to IC4 (source drivers) and IC5 (gate driver). And, by applying the driving signal to source lines and gate lines through the wiring patterns (not shown) provided on the liquid crystal display panel 1, an image according to the driving signal is displayed on the display region 2 of the liquid crystal display panel 1.
Recently, the source drivers and the gate drivers provided on the liquid crystal display panel 1 have increased as definition of a screen of the liquid crystal display device becomes higher. And, when the source drivers and the gate drivers increase, the electrode terminals R1 to Rn and T1 to Tn formed on the liquid crystal display panel 1 and the printed circuit board PCB1, respectively, increase, for example. Correspondingly, the wiring patterns P1 to Pn of the flexible printed circuit board FPC1 for electrically connecting the printed circuit board PCB1 and the liquid crystal display panel 1 also increase, for example. On the other hand, it is required to provide a smaller liquid crystal display module L for obtaining a smaller image display device. Therefore, recently, each of the electrode terminals provided on the liquid crystal display panel 1 and the printed circuit board PCB1 tends to be finely formed, and each of the wiring patterns of the flexible printed circuit boards FPC1 to FPC4 tends to be formed by fine patterns. In this case, however, by using a conventional process in which the alignment between the liquid crystal display panel 1 and the flexible printed circuit boards FPC1 to FPC4 is performed by using the circular reference markers N1 and the circular alignment markers N2, a problem might arise in the electrical connection between the liquid crystal display panel 1 and the printed circuit board PCB1 when rotational misalignment beyond tolerance occurs in θ direction around Z-axis. Hereinafter, the problem which might arise when the rotational misalignment beyond tolerance in θ direction around Z-axis occurs in the flexible printed circuit board FPC1 is described in detail with reference to FIGS. 15(a) and 15(b).
FIGS. 15(a) and 15(b) are views illustrated in association with the schematic views shown in FIGS. 13(a) and 13(b), schematically showing a condition in which the rotational misalignment beyond tolerance in θ direction around Z-axis occurs in the flexible printed circuit board FPC1, in which FIG. 15(a) is a plan view and FIG. 15(b) is a cross-sectional view taken along A-A′ line in FIG. 15(a). The flexible printed circuit board FPC1 is perspectively shown as in FIGS. 13(a), 13(b) and FIGS. 14(a), 14(b). X-axis, Y-axis, and Z-axis directions in FIGS. 15(a) and 15(b) are defined as shown in the drawings (Z-axis direction is a direction perpendicular to the drawing surface).
As appreciated from FIGS. 15(a) and 15(b), when the flexible printed circuit board FPC1 greatly rotates in θ direction around Z-axis, and is bonded to the liquid crystal display panel 1 such that the reference markers N1 are located inward relative to and in contact with the alignment markers N2, a problem that the electrode terminals T1 to Tn of the printed circuit board PCB1 and the wiring patterns P1 to Pn of the flexible printed circuit board FPC1 are not properly electrically connected to each other might arise when the flexible printed circuit board FPC1 is bonded to the printed circuit board PCB1. In FIGS. 15(a) and 15(b), specifically, the conductive patterns Pn and Pn-1 of the flexible printed circuit board FPC1 are positioned outside the anisotropic conductive adhesive 4B provided on the printed circuit board PCB1, and therefore, are not electrically connected to the electrode terminals Tn and Tn-1 of the printed circuit board PCB1.
Therefore, there has been a problem that the conventional circular reference markers N1 and alignment markers N2 for alignment can not cope with the misalignment beyond tolerance in a rotational direction. This has been significant, especially when the flexible printed circuit board FPC1 is elongated in Y-axis direction. This is because, even if the misalignment of the flexible printed circuit board FPC1 in X-axis direction occurring when this rotates in θ direction around Z-axis is small on the liquid crystal display panel 1 side, the misalignment increases in proportion to a length of the flexible printed circuit board FPC1 in Y-axis direction, on the printed circuit board PCB1 side.